Microarrays are known in the art and are commercially available from a number of sources. Microarrays have been used for a number of analytical purposes, typically in the biological sciences. An array is essentially a two-dimensional sheet where different portions or cells of the sheet have different biomolecule elements, such as, nucleic acids or peptides, bound thereto. Microarrays are similar in principle to other solid phase arrays except that assays involving such microarrays are performed on a smaller scale, allowing many assays to be performed in parallel. For example, the reactive biomolecules bound to a chip.
Biochemical molecules on microarrays have been synthesized directly at or on a particular cell on the microarray, or preformed molecules have been attached to particular cells of the microarray by chemical coupling, adsorption or other means. The number of different cells and therefore the number of different biochemical molecules being tested simultaneously on one or more microarrays can range into the thousands. Commercial microarray plate readers typically measure fluorescence in each cell and can provide data on thousands of reactions simultaneously thereby saving time and labor. A representative example of the dozens of patents in this field is U.S. Pat. No. 5,545,531.
Currently two dimensional arrays of macromolecules are made either by depositing small aliquots on flat surfaces under conditions which allow the macromolecules to bind or be bound to the surface, or the macromolecules may by synthesized on the surface using light-activated or other reactions. Previous methods also include using printing techniques to produce such arrays. Some methods for producing arrays have been described in “Gene-Expression Micro-Arrays: A New Tool for Genomics”, Shalon, D., in Functional Genomics: Drug Discovery from Gene to Screen, IBC Library Series, Gilbert, S. R. & Savage, L. M., eds., International Business Communications, Inc., Southboro, Mass., 1997, pp 2.3.1.-2.3.8; “DNA Probe Arrays: Accessing Genetic Diversity”, Lipshutz, R. J., in Functional Genomics: Drug Discovery from Gene to Screen, IBC Library Series, Gilbert, S. R. & Savage, L. M., eds., International Business Communications, Inc., Southboro, Mass., 1997, pp 2.4.1.-2.4.16; “Applications of High-Throughput Cloning of Secreted Proteins and High-Density Oligonucleotide Arrays to Functional Genomics”, Langer-Safer, P. R., in Functional Genomics: Drug Discovery from Gene to Screen, IBC Library Series, Gilbert, S. R. & Savage, L. M., International Business Communications, Inc., Southboro, Mass., 1997, pp 2.5.13; Jordan, B. R., “Large-scale expression measurement by hybridization methods: from high-densities to “DNA chips””, J. Biochem. (Tokyo) 124: 251-8, 1998; Hacia, J. G., Brody, L. C. & Collins, F. S., “Applications of DNA chips for genomic analysis”, Mol. Psychiatry 3: 483-92, 1998; and Southern, E. M., “DNA chips: Analyzing sequence by hybridization to oligonucleotides on a large scale”, Trends in Genetics 12: 110-5, 1996.
Regardless of the technique, each microarray is individually and separately made, typically is used only once and cannot be individually precalibrated and evaluated in advance. Hence one depends on the reproducibility of the production system to produce error-free arrays. These factors have contributed to the high cost of currently produced biochips or microarrays, and have discouraged application of this technology to routine clinical use.
For scanning arrays, charged coupled device (CCD) cameras are widely used. The cost of these has declined steadily, with suitable cameras and software now widely available. However, in one proposed variation, an array is located at the ends of a bundle of optical fibers with the nucleic acid or antibody/antigen attached to the end of the optical fiber. Detection of fluorescence may then be performed through the optical fiber, see U.S. Pat. No. 5,837,196.
Fiber optical arrays are routinely produced in which glass or plastic fibers are arrayed in parallel in such a manner that all remain parallel, and an optical image may be transmitted through the array. Parallel arrays may also be made of hollow glass fibers, and the array sectioned normal to the axis of the fibers to produce channel plates used to amplify optical images. Such devices are used for night vision and other optical signal amplification equipment. Channel plates have been adapted to the detection of binding reactions (U.S. Pat. No. 5,843,767) with the individual holes being filled after sectioning of the channel plate bundle, and discrete and separate proteins or nucleic acids being immobilized in separate groups of holes.
Hollow porous fibers have been widely used for dialysis of biological samples, in kidney dialyzers and for water purification. Methods for aligning them in parallel arrays, for impregnating the volume between them with plastic, and for cutting the ends of such arrays have been described (see, for example, U.S. Pat. No. 4,289,623).
Immobilized enzymes have been prepared in fiber form from an emulsion as disclosed in Italy Pat. No. 836,462. Antibodies and antigens have been incorporated into solid phase fibers as disclosed in U.S. Pat. No. 4,031,201. A large number of other different immobilization techniques have been used and are well known in the fields of solid phase immunoassays, nucleic acid hybridization assays and immobilized enzymes, see, for example, Hermanson, Greg, T. Bioconjugate Techniques. Academic Press, New York. 1995, 785 pp; Hermanson, G. T., Mallia, A. K. & Smith, P. K. Immobilized Affinity Ligand Techniques. Academic Press, New York, 1992, 454 pp; and Avidin-Biotin Chemistry: A Handbook. D. Savage, G. Mattson, S. Desai, G. Nielander, S. Morgansen & E. Conklin, Pierce Chemical Company, Rockford Ill., 1992, 467 pp.
Scanners and CCD cameras have been described to detect and quantitate changes in fluorescence or adsorbence and are suitable for existing biochips. These, together with suitable software, are commercially available.
Currently available biochips include only one class of immobilized reactant, and perform only one class of reactions. For many types of clinical and other analyses there is a need for chips which can incorporate in one chip reactants immobilized in different ways.